1. Field of the Invention
The present invention relates to a data playback device in order to playback data recorded on a data recording medium, such as an optical disk and the like.
2. Description of the Related Art
A playback device for a compact disk (CD) is an example of a known data replay device.
FIG. 9 is a diagram showing the constitution of a CD. As shown in FIG. 9, a CD has a spiral array of phase pits 82 of relief form in a transparent substrate 81 of thickness 1.2 mm. This is a data track. Voice data is then recorded by causing voice data to correspond to the length of the phase pits.
When the data recorded on a CD is played back in a playback device, first, the CD is rotated. By using an illuminating light beam, a light spot of smaller radius than the phase pits is then formed on the record tracks. Data is then replayed by detecting the diffraction state of the reflected light of the light spot on the record track.
When the light spot is in a position with no phase pit, all of the reflected light from the record track returns to the playback head. Because of this, a data detector built into a playback head of a playback device detects a large value. When a phase pit is in the position of the light spot, the light reflected from the record track is diffracted by the phase pit. Because of this, a portion of the reflected light is reflected to the exterior and does not return to the playback head. The remaining portion of the reflected light returns to the playback head. Namely, when a phase pit is in the position of the light spot, the data detector built into the playback head detects a small value.
Generally, the radius of the light beam from the playback head can be narrowed down to the diffraction limit. Because of this, when a data playback head is used with a built-in laser light source having a wavelength of 830 nm, the radius of the light spot illuminating the data track can be narrowed down to 1 .mu.m or less. Accordingly, the pitch of the data tracks can be 1.6 .mu.m, and a large amount of data can be recorded.
Examples of other data playback devices are magnetooptical disk devices or phase change disk devices.
The playback principle of these devices, except for using the Kerr rotation effect or the reflectivity change effect of the light reflected from the data recording medium, is the same as that of the CD playback device, and a detailed description is omitted.
The demand for recording more data on a data recording medium is very high. In response to this demand, it was generally proposed by the inventors and in their investigations to make the playback beam diameter smaller by making the wavelength of the light source of the playback head short.
However, there are limitations on the wavelength of the light source of the playback head. That is, the wavelength cannot be made infinitely short. On the other hand, when the size of the playback beam is fixed and the tracks are narrowed, the light spot due to the playback beam also illuminates record pits of the adjacent tracks. As a result, a problem was that data of the adjacent tracks was also read out, in addition to the data of the subject playback track.
Consequently, a data playback device is required which can play back only the data from the subject track, suppressing data readout from adjacent tracks.
An important result of the inventors' investigations was the discovery of the land/groove playback method as a countermeasure to suppress data readout from adjacent tracks. The tracks of magnetooptical and the like recording media are generally formed as grooves in concentric circles or spirals. Accordingly, convex portions and concave portions exist on the record surface. In the recording media heretofore, data were recorded on either the convex or the concave portions. In contrast to this, in the land/groove playback method, disks are used on which data has been recorded on both the convex portions (lands) and the concave portions (grooves).
This is a superior method, because the track pitch can be practically halved. The results in suppressing data readout from adjacent tracks by the land/groove method have been described in the following literature and references, and a detailed description will be omitted here.
Technology in relation to phase change disks is mentioned in "High Density Phase Change Disks By Land & Groove Recording" (Fifth Phase Change Recording Research Society Symposium, Collected Papers"). Moreover, technology related to magnetooptical disks is described in "Crosstalk Analysis of Land/Groove Magnetooptical Recording" (Symposium on Optical Memory 1994).
Furthermore, the present assignee's Japanese patent applications 6-190695, 6-215137, and 6-215138 also describe the effect of suppressing data readout from adjacent tracks in land/groove playback methods. Nevertheless, because there exist two kinds of tracks, land tracks and groove tracks, in this land/groove playback method, data could not be freely played back from optional tracks by the prior art technology.
For example, when playing back data from a recording medium, by causing the light spot to move relatively, the data recorded on the data track is played back in succession. Specifically, in playing back a CD, in the state in which the disk is caused to rotate, the illumination position of the light spot is controlled such that the light spot is normally on the data track. This kind of control is called tracking control.
The tracking control mechanism in prior art devices could only correspond to tracking with respect to either one of land tracks or groove tracks, not both. The reason for this is that, because the tracking characteristics differ in land tracks and groove tracks, when tracking control is matched to the track characteristics of one kind, i.e., land or groove tracks, tracking control is not suitable for the tracking control of the other kind of tracks, groove or land tracks.